Microsoft has confirmed that hackers are targeting a new vulnerability that could lead to arbitrary code execution.

In an advisory, Microsoft described how the bug can be exploited using a specially crafted Excel document. The malicious Excel file attempts to access an invalid object, allowing the attacker to execute arbitrary code.

According to Microsoft, the vulnerability is currently being exploited in "limited and targeted attacks." The advisory addresses Microsoft Office 2000, Office 2002, Office 2003, Office 2007, Office 2004 for Mac and Office 2008 for Mac.

If a user is logged on with administrative user rights, an attacker could take complete control of the affected system, gaining the ability to install programs and view, change or delete data, Microsoft warned.

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